1. Field of the Invention
The present invention relates to a rotation angle detecting device that employs Hall elements, whose temperature characteristic can be corrected.
2. Description of the Related Art
A well-known rotation angle detecting device employs one or more Hall elements, which are disposed in a magnetic field formed by a permanent magnet. The Hall elements are arranged to rotate relative to the permanent magnet as a rotating object rotates, so that the output voltage of the Hall elements is generated in response to change in magnetic flux density. The rotation angle of the rotating object is calculated based on the output voltage of the Hall elements. JP-A 2001-124511 or U.S. Pat. No. 6,498,479 B1, which is a counterpart U.S. patent, discloses a rotation angle detecting device in which temperature characteristic of the output voltage of the Hall elements is corrected.
Assuming that: the ambient temperature of the rotation angle detecting device is t; the output voltage of the Hall element under the ambient temperature t is Vout(t); the offset voltage of the Hall element when the magnetic flux density is zero is Voff(t); and the inclination of the output voltage to the magnetic flux density (herein after referred to as sensitivity) is S(t), the output voltage of the Hall element Vout(t) can be expressed as follows.Vout(t)=Voff(t)+B×S(t)  (1)
Usually, temperature characteristic is corrected by setting the sensitivity S(t), which is set at a specific magnetic flux density.
However, it is difficult to accurately correct the temperature characteristic of the Hall element disposed in the magnetic field of a magnetic flux density that is different from the specific magnetic flux density.